Update actions/setup-python action to v3 (#324)

Signed-off-by: Renovate Bot <bot@renovateapp.com>

Author: renovate[bot]

.github/workflows/lint-test.yml

@@ -20,7 +20,7 @@ jobs:
       # Python is required because `ct lint` runs Yamale (https://github.com/23andMe/Yamale) and
       # yamllint (https://github.com/adrienverge/yamllint) which require Python
       - name: Set up Python
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@v3
         with:
           python-version: 3.7